Damian Green, one of Theresa May’s closest allies, has resigned from the cabinet after an investigation found he had breached the ministerial code.
He quit after he was found to have made “inaccurate and misleading” statements about what he knew about claims pornography had been found on a computer in his Commons office in 2008.
In his resignation letter, Mr Green apologised for his actions.
BBC’s Laura Kuennsberg said the PM “had little choice but to ask him to go”.
In her written response, Mrs May expressed “deep regret” at his departure.
Mr Green, who as first secretary of state was the PM’s deputy, had been under investigation regarding allegations of inappropriate conduct.
He denied suggestions that he made unwanted advances to a female journalist, Kate Maltby, in 2015 and viewed pornography on a computer in his Commons office in 2008.
An official report by the Cabinet Office found that statements he had made about being unaware pornographic material had been found on his computer were “inaccurate and misleading” and as such fell short of the ministerial code.
The report also found that although there were “competing and contradictory accounts of what were private meetings” between himself and Ms Maltby, the investigation found her account “to be plausible”.
Her parents, Colin and Victoria Maltby, said in a statement they were not surprised to find that the inquiry found Mr Green to have been “untruthful as a minister, nor to that they found our daughter to be a plausible witness”.
They praised their 31-year-old daughter for her courage in speaking out about the “abuse of authority”.
Ms Maltby is not commenting on Mr Green’s resignation until she receives more details from the Cabinet Office.
In his letter, Mr Green said he accepted statements he made about what he knew about the pornography investigation could have been “clearer”, conceding his lawyers had been informed about the original discovery in 2008 and the police had raised the matter within him in a phone call in 2013.
“I apologise that my statements were misleading on this point,” he said.